Field of the Invention
This invention generally relates to time synchronization in computer systems. More specifically, the invention relates to methods and systems that are particularly well suited for maintaining time synchronization among plural interconnected computer systems.
Background Art
Over the past several years, computer manufacturers have begun to provide processing architectures based on a multi-system shared data approach. In these architectures, multiple large-scale computer systems are interconnected, through, for example, a coupling facility or other interprocessor communication mechanism, which permits shared memory or shared data. The resulting interconnected complex of computers is commonly referred to as a sysplex (for “system complex”).
One important challenge in the design and operation of interconnected, complex computer systems, such as a sysplex, is to maintain all the component systems time synchronized.
Clustered computer systems commonly maintain synchronized time-of-day (TOD) clocks. This common TOD is used to manage distributed tasks among the systems. For example, the common TOD may be used to obtain unique identifiers among the processors, to provide timestamp values for data objects, to provide serialization among distributed tasks, etc. Among systems that are physically close together, the TOD synchronization must be quite accurate. In the past, this has been accomplished through the use of specialized hardware that provides time synchronization signals to all of the clustered processors. As processor speeds increase, the specialized hardware becomes inadequate to the task of close synchronization. In addition, the external time reference (ETR) architecture of the prior art has distance limitations (<40 km) and requires dedicated cabbing and external ETR boxes.